1. Field of the Invention
The present invention relates to a field emission display, and more particularly, to a field emission display having carbon-based emitters.
2. Description of the Related Art
A field emission display (FED) uses a cold cathode as the source for emitting electrons. The overall quality of the FED depends on the characteristics of emitters, which form an electron emission layer. In the initial FEDs, the emitters were formed of what are referred to as Spindt-type metal tips (or microtips). A main material of the metal tips is molybdenum (Mo).
However, in the FED having metal tip emitters, since (a) extremely fine holes in which the emitters are disposed must be formed in an insulating layer, and (b) the metal tips must be formed uniformly over the entire display area of the FED using the process of depositing molybdenum (MO), production is complicated. Further, not only is high technology needed, but expensive equipment is required for the manufacture of the FED such that unit costs are increased. Such factors make production of large screens of these types of FEDs difficult.
Accordingly, a great deal of research and development is being performed by those in industries related to FEDs to form emitters in a flat configuration that both enables electron emission at low voltages, and simplifies manufacture. It is known that carbon-based materials (e.g., graphite, diamond, DLC (diamond-like carbon), C60 (Fullerene), or CNT (carbon nanotubes)), are suitable for use in the manufacture of planar emitters. In particular, it is believed that CNTs, with their ability to enable relatively low driving voltages, are the ideal material for emitters in field emission displays.
Typically during the manufacture of an FED having a triode structure including a cathode, an anode, and a gate electrode, the cathode electrodes are first formed on a substrate. An insulating layer having minute holes and gate electrodes are formed on the cathode electrodes. The emitters are then formed in the holes and over the cathode electrodes.
In the above triode structure, however, color purity deteriorates and the realization of sharp pictures is difficult during actual operation. This deterioration is caused by an increase in a divergent force on electron beams, which are formed of electrons emitted from the emitters. The divergent force is formed by a voltage (a positive voltage of a few to a few tens of volts) applied to the gate electrodes such that the electron beams do not travel along their intended paths. Therefore, the electron beams land not only on intended phosphor layers, but also on unintended phosphor pixels of the wrong color to illuminate the same.
To overcome this problem, there are efforts to minimize the diffusion of the electron beams by decreasing an area of the emitters corresponding to each of the phosphor pixels. However, there are limitations as to how small the emitters can be formed and still realize good formation. Also, when the whole area of the emitters are formed excessively small, there is a reduction in the ability to focus the electron beams to within the phosphor pixels.
Alternatively, to prevent the problem of excessive diffusion of the electron beams, there have been attempts to form separate electrodes for electron beam focusing in peripheral portions of the gate electrodes. However, there are limited effects when the FED has emitters of the microtip. Further, there are inherent problems during manufacture as a result of the microtip formation of the emitters.
U.S. Pat. No. 5,552,659 discloses an electron emitting source structure in which a ratio between a thickness of a non-insulating layer and a dielectric layer, which are formed on a substrate on which emitters are provided, and a ratio between a diameter of holes formed passing through the non-insulating layer, the dielectric layer, and a gate layer, which is formed on the dielectric layer, and the thickness of the non-insulating layer are limited to reduce the divergence of electron beams. In this device, a plurality of electron emitting sources is minutely formed within a plurality of the holes, each pair of electron emitting sources and holes being formed corresponding to one pixel. Accordingly, manufacture is difficult due to the extremely complicated structure. Also, since there are structural restrictions as to space during actual manufacturing, there are limits to maximizing the number and area of the emitters corresponding to each pixel such that it is difficult to realize a high resolution of the FED. In addition, because of the increasing load after being operated for long periods, the life reliability of the FED is reduced.